Do not show unpublished proposals on the homepage

The chances of an unpublished proposal appearing on the homepage was
very low because only the proposals with the most votes appear there and
unpublished proposals don't have any votes. However, it was technically
possible on new sites where only a few proposals had been created.

app/models/widget/feed.rb

@@ -21,7 +21,7 @@ class Widget::Feed < ApplicationRecord
   end
 
   def proposals
-    Proposal.sort_by_hot_score.limit(limit)
+    Proposal.published.sort_by_hot_score.limit(limit)
   end
 
   def debates

spec/models/widget/feed_spec.rb

@@ -28,6 +28,14 @@ describe Widget::Feed do
 
         expect(feed.proposals).to eq([best_proposal, medium_proposal, worst_proposal])
       end
+
+      it "does not return unpublished proposals" do
+        create(:proposal, :draft, title: "Draft proposal")
+
+        feed = build(:widget_feed, kind: "proposals")
+
+        expect(feed.proposals).to be_empty
+      end
     end
 
     describe "#debates" do